Food biochem and food safety

What are microorganisms?

Microorganisms are tiny organisms that can only be seen with a microscope. These include yeasts, moulds and bacteria.

Why do we cook food?

- Safety: cooking reduces chance of food-borne illness by killing harmful bacteria

- Flavour: it enhances flavour through chemical reactions

- Nutrition: cooking makes it easier for the body to get its nutrients - it breaks down proteins

- Preservation: cooking can increase shelf-life of food by destroying bacteria and mould

- Digestibility: it makes food easier to chew, swallow, and digest.

What do yeasts, moulds, and bacterias need to grow?

4 conditions: food, moisture, warmth, time

Chemical raising agents

Chemical raising agents produce carbon dioxide gas through chemical reactions when mixed with moisture, heat or acidic ingredients.

Example of chemical raising agents

Baking soda reacts with acidic ingredients (vinegar, buttermilk) to release carbon dioxide

Biological raising agents

This raising agent uses living microorganisms like yeast to produce carbon dioxide through fermentation.

Example of biological raising agents

Yeast: feeds on sugars in the dough and produces carbon dioxide and alcohol as byproducts. The carbon dioxide gets trapped in the dough, causing it to rise. When baked the heat kills the yeast, expands the trapped gas and evaporates the alcohol

Physical raising agents

Physical raising agents rely on incorporating air or steam through mechanical actions or heat.

Examples of physical raising agents

Folding traps air in batters. High temps turn liquid to steam, which expands and raises mixtures like puff pastry or choux

What is fermentation?

Fermentation is a metabolic process in which microorganisms, such as yeast and bacteria, break down sugars into simpler compounds like carbon dioxide, alcohol, and organic acids.

How should food be stored?

Keep food in the fridge to stop/slow bacterial growth. Store raw meats on the bottom shelf to avoid dripping and cooked food on the top. Use sealed containers, check leftovers regularly, and always separate raw and cooked food to prevent contamination.

What is cross contamination and how can it happen to food?

It is the transfer of harmful bacteria, viruses, allergens or other microorganisms from one object, surface or food to another. For example, utensils not cleaned properly, sneezing on food.

What are preservatives?

Preservatives are food additives added to to prevent decomposition and extend shelf life.

2 main types of preservatives

Natural preservatives: from natural sources - salt, sugar, vinegar

Artificial preservatives: synthesised compounds, benzoates, sorbates, nitrates

How does food spoilage happen? Give multiple factors

The main cause of food spoilage is when food is contaminated by yeast, moulds, or bacteria, making it unsafe to eat.

Food spoilage may also be caused by enzyme activity, causing colour and flavour changes as well as over-ripening of some fruits and vegetables.

There are various other factors that cause food spoilage, such as light, oxygen, heat, humidity, temperature

Solute vs solvent

A solute is the substance that is dissolved in a solution (salt) while the solvent is the substance in which the solute dissolves (water). Together they form a solution.

What are enzymes?

Biological catalysts that break down large molecules into smaller, absorbable components.

Used in food production to improve digestion, ripening, and texture.

What are yeasts?

Yeasts are eukaryotic, single-celled microorganisms that are member of the fungus kingdom. They reproduce by budding.

Ideal growth conditions for yeasts

Most grow best in the presence of oxygen (aerobic) but some can survive without it (anaerobic). Yeasts grow best in conditions around 25-30˚C. They need moisture for growth as well as glucose/sugar and prefer acid foods that are fairly moist. They can also grow in high concentrations of sugar and salt.

What does yeast do?

Yeast is found in nature and within our bodies; it consumes sugar and produces by-products such as carbon dioxide, alcohol, and other chemical compounds. Yeast is an essential ingredient in baking, brewing, and winemaking.

Which foods do yeasts often spoil?

Yeasts can spoil food such as jam, honey, fruit, yoghurts and fruit juices. They ferment the sugars in these foods, which produces carbon dioxide gas and alcohol. This causes food spoilage. The food will develop 'off' flavours and may appear 'fizzy'.

What are moulds?

Moulds are tiny multicellular fungi, which produce threadlike filaments. These filaments help the mould to spread around the food, extracting nutrients from it.

Ideal growth conditions for moulds

Moulds may be different colours and grow on many foods, including acid and alkaline foods as well as those with high sugar and salt concentrations. They grow best between 20°C and 30°C, although they can also grow at low temperatures, including in the fridge. High humidity and fluctuating temperatures can speed up mould growth. Although moulds do require some moisture to grow, they can grow on fairly dry foods such as hard cheeses.

Mould growth can be slowed down or prevented by:

- storing food in a cool, dry place (for example, kitchen cupboard)

- storing food in the fridge

- heating/cooking food

- storing in acid conditions (for example, pickled onions).

Which foods do moulds often spoil?

Moulds often grow on and spoil bread and bakery products. Some breads have preservatives added to prevent mould growth.

Moulds may also spoil cheeses in vacuum packs if the seal is broken. Foods spoiled with mould should not be consumed, even if the visible mould is scraped off. The mould may have spread harmful substances that are not visible deep into the food.

What are bacteria?

Bacteria are single-celled microorganisms. They can be divided into three groups:

- harmless bacteria

- pathogenic bacteria

- food spoilage bacteria.

Ideal growth conditions for bacteria

Bacteria need food, warmth, moisture and time to grow. Bacteria do not like acidic conditions;

They grow best in neutral conditions. This means neither acid nor alkaline conditions.

Bacterial growth can be slowed down or prevented by:

- storing perishable food in the fridge at between 0°C and below 5°C

- cooling cooked perishable food to room temperature within 90 minutes before putting in the fridge

- reheating leftover food only once (any remaining food should be thrown away)

- using high concentrations of salt (e.g. for bacon), sugar (e.g. for jam) and acid (eg. for pickled eggs) to destroy most bacteria.

What are high-risk foods, and why are they more prone to bacterial growth?

High-risk foods are foods that are ready to eat without further heating or cooking. Bacteria prefer foods with a high protein content that are moist. These foods provide excellent conditions for bacterial growth, especially if kept in warm conditions.

Most cases of food poisoning are caused by consuming high-risk foods contaminated with pathogenic bacteria. Examples of high-risk foods are:

- cooked meat and poultry

- cooked meat products such as gravy, soup and stock

- milk and eggs and dishes made from them, for example unpasteurised soft cheese

- eggs and dishes made from them, for example homemade mayonnaise

- shellfish such as mussels, crabs and lobsters

- cooked rice

Why does too much heat or cold destroy yeast?

Heat: yeasts die about 55˚C up because at these temperatures, the protein within yeast cells lose their structure, causing cellular functions to stop - you kill them

Cold: below 10˚C, yeast metabolism slows down considerably. Using cold water, it extends the time required for dough to rise due to yeast enzymes being inactive and preventing the metabolic breakdown of sugars necessary for fermentation - the yeast will not be activated

What is budding?

Budding is a type of asexual reproduction in which a new organism is formed from a bud of an existing organism. The new organism remains attached to the parent organism till it gets matured.

How can preservatives be used?

Antimicrobial preservatives: Prevent the growth of bacteria, mould, and yeast.

- Salt: Used in cured meats like bacon and salted fish.

- Vinegar: Common in pickled vegetables (e.g., cucumbers, onions).

- Sorbic acid: Found in cheeses, baked goods, and fruit juices.

Sodium benzoate: Used in soft drinks, salad dressings, and jams.

- Sodium nitrate: Added to processed meats like ham and sausages to prevent bacterial growth.

Antioxidant preservatives: Prevent oxidation, which can cause rancidity and spoilage.

- Ascorbic acid (Vitamin C): Prevents browning in cut fruits and is added to fruit juices.

- Tocopherols (Vitamin E): Found in vegetable oils, cereals, and margarine.

- BHA & BHT: Used in snacks, chips, and processed meats to prevent fat oxidation.

What is oxidation?

Oxidation is the loss of water-soluble vitamins on exposure to heat/air.

Long explanation: Enzymes can cause foods to spoil by the process of oxidation. Oxidation can be used to describe the loss of the water-soluble vitamins (B group and vitamin ©) from some fruits and vegetables during food preparation and cooking processes.

Types of Yeast

Dry yeast: Comes in a dormant state and needs to be activated with warm water.

- Instant yeast does not require activation and can be mixed directly into the dough.

- Yeast cells will not activate with cold water.

- Boiled water kills yeast cells.

- Yeast feeds on sugar, which helps it grow.

Wet yeast: Also known as fresh yeast, has a higher moisture content and is often used in professional baking. It must be stored in the refrigerator and has a shorter shelf life than dry yeast.

Proofing

The process of letting dough rise due to yeast fermentation. The carbon dioxide produced causes the dough to expand, leading to a lighter texture.

Temperature and humidity affect proofing time.

Good and bad mould

Good: Used in blue cheese and some fermented foods.

Bad: Causes food spoilage and can produce harmful mycotoxins, which may lead to health issues when consumed.

What are 3 types of contamination in food?

Biological Contamination

Occurs when bacteria, viruses, or parasites contaminate food.

Bacteria multiply rapidly, leading to food-borne illnesses such as Salmonella, E. coli, and Listeria.

Chemical Poisoning

Caused by chemical residues from pesticides, cleaning agents, or heavy metals in food.

Can be fatal if medical attention is not received promptly.

Bacterial Contamination

Occurs when food is exposed to bacteria such as Staphylococcus aureus or Campylobacter.

How to prevent biological contamination

Proper hygiene, storage, and cooking temperatures help prevent contamination.

How to prevent bacterial poisoning

Can be prevented by proper cooking, refrigeration, and avoiding cross-contamination.

What are food additives?

A substance added to food to enhance its flavour or appearance or to preserve it.

Pros and cons of preservatives

Pros:

Extend shelf life and maintain food quality.

Slows or prevents changes in flavour, texture, and colour.

Reduce food waste by preventing spoilage.

Cons:

Can reduce nutritional value if overused.

Some additives may have long-term health risks.

Why we eat

To obtain essential micronutrients (vitamins and minerals) necessary for growth and development.

Food provides energy, aids in cellular repair, and supports bodily functions.

Pros and cons of canned foods

Pros:

- Long shelf life.

- Convenient and easy to store.

- Prevents food spoilage by sealing out bacteria.

Cons:

- Loss of certain vitamins due to high-temperature processing.

- Potential exposure to BPA from can linings.

What are micronutrients?

Micronutrients are vitamins and minerals needed by the body in very small amounts for growth and development

Why is plastic packaging bad

- Non-biodegradable: Most plastic takes hundreds of years to decompose, leading to land and ocean pollution.

- Microplastic pollution: Over time, plastic breaks down into tiny particles that contaminate soil, water, and even food chains, harming both wildlife and human health.

- Harm to marine life: Plastic waste in oceans can be mistaken for food by marine animals, leading to injury or death.

- Chemical leaching: Some plastics contain harmful chemicals like BPA, which can seep into food and beverages, potentially affecting health.

- High carbon footprint: Plastic production and disposal require fossil fuels and generate greenhouse gas emissions, contributing to climate change.

- Recycling challenges: While recycling exists, many plastics are difficult or expensive to recycle, leading to low recycling rates and more waste in landfills.